What kind of ruins would an intelligent energy being leave behind

I am currently working on a system brief for the New Streel system ( http://www.starfrontiers.us/node/9273 ) and I am populating it with the ruins of a race of energy beings. This race, which the Frontier colonists are calling the &quot;Brights,&quot; had colonized the planet Corpco back during the time of the Tetrarch Societies and were driven to near extinction by another vampire-like energy creature.<br /><br />I am basing the Brights off of an unnamed race created by William Douglass in Star Frontiersman issue 18, pp. 19-20, though I am giving them a few different abilities. They won't communicate by telepathy but rather by radio waves and flashes of light.<br /><br />So, what kind of ruins would such a race have?